Self-repairing, reinforced matrix materials

ABSTRACT

Self-repairing, fiber reinforced matrix materials include a matrix material including inorganic as well as organic matrices. Disposed within the matrix are hollow fibers having a selectively releasable modifying agent contained therein. The hollow fibers may be inorganic or organic and of any desired length, wall thickness or cross-sectional configuration. The modifying agent is selected from materials capable of beneficially modifying the matrix fiber composite after curing. The modifying agents are selectively released into the surrounding matrix in use in response to a predetermined stimulus be it internal or externally applied. The hollow fibers may be closed off or even coated to provide a way to keep the modifying agent in the fibers until the appropriate time for selective release occurs. Self-repair, smart fiber matrix composite materials capable of repairing microcracks, releasing corrosion inhibitors or permeability modifiers are described as preferred embodiments in concrete and polymer based shaped articles.

This is a continuation of application Ser. No. 08/537,228, filed Sep.29, 1995, now U.S. Pat. No. 5,660,624, issued Aug. 26, 1997, which is inturn a continuation of application Ser. No. 08/189,665, filed Feb. 1,1994, now U.S. Pat. No. 5,427,880, which is in turn acontinuation-in-part of U.S. Ser. No. 08/174,751, filed Dec. 29, 1993,now U.S. Pat. No. 5,575,841, issued Nov. 19, 1996, which is in turn acontinuation of U.S. Ser. No. 07/540,191, filed Jun. 19, 1990 abandoned.

BACKGROUND OF THE INVENTION

The present invention generally relates to matrix materials for use in awide variety of end use fields and applications. More particularly, theinvention relates to new and improved self-repairing, settable orcurable matrix material systems containing so-called smart-release fiberreinforcements, alone or in combination with other reinforcement. Myprior parent application, Ser. No. 540,191, filed Jun. 19, 1990,describes the new and improved inorganic and organic matrix compositesemploying concrete matrix systems and asphalt matrix systems asillustrative embodiments. That prior application describes smart-releasehollow fiber additives in settable construction materials andthermoplastic matrices, such as asphalt. This application is being filedto describe other embodiments of the smart-release matrix compositematerials generally described in my earlier application and to provideadditional examples of end use applications to which these new andimproved compositions, articles and methods may be specially adapted andused.

Cement is a fine, gray powder consisting of alumina, lime, silica andiron oxide which sets to a hard material after mixture with water.Cement, along with sand and stone aggregate, make up concrete, the mostwidely used building material in the world. Steel reinforcing bars(rebars) are commonly added to the interior of concrete for additionalstrength.

There are many reasons for the popularity of concrete. It is relativelyinexpensive, capable of taking on the shape of a mold, has exceptionallyhigh compression strength and is very durable when not exposed torepeated freeze-thaw cycles. However, as a building or constructionmaterial, concrete, whether it is reinforced or not, is not without someshortcomings. One major drawback of concrete is that it is relativelylow in tensile strength. In other words, it has little ability to bend.Concrete also has little impact resistance and is frequently brittle. Athird major drawback is that its durability is significantly reducedwhen it is used in applications which require it to be exposed torepeated freeze-thaw cycles in the presence of water. Concrete isrelatively porous and water is able to permeate the material. Freezingand thawing with the accompanying expansion and contraction of thewater, forms cracks in the concrete. Furthermore, if salt is alsopresent in the environment, it dissolves in the water and permeates intothe concrete where it is capable of inducing corrosion in any of therebars or other metallic reinforcements present.

Various techniques have been suggested in the past for overcoming thesedrawbacks. The addition of fibers to concrete has improved its tensilestrength but has decreased its compression strength. Providing exteriorcoatings on the outer surfaces of the concrete has reduced waterpermeation, but it is a time-consuming additional step and has little,if any, effect on the lasting strength of the concrete. The addition ofmodifying agents as freely-mixed additives into a concrete mixturebefore setting has also been tried. These efforts have met withgenerally unsatisfactory results. Attempts to add modifying agents inthe form of micronodules or prills have also been tried. Frequently, theprills are designed to be heat melted to cause release of the modifyingagent into the matrix after setting of the materials. These designsrequire the application of heat to release the beneficial additive intothe matrix after cure. Moreover, the melted, permeated agents leavebehind voids in the concrete which weakens the overall structure underload. Accordingly, a demand still exists for an improved concrete matrixmaterial having greater tensile strength, greater durability andcomparable or improved compression strength.

In addition to cementitious building materials, the use of polymercomposites as structural materials has grown tremendously in recentyears. Polymer composite materials have advantages over steel orconcrete including good durability, vibration damping, energyabsorption, electromagnetic transparency, toughness, control ofstiffness, high stiffness to weight ratios, lower overall weight andlower transportation cost. These polymer matrix materials comprise acontinuous polymer phase with a fiber reinforcement therein. Somepolymer composite materials are three times stronger than steel and fivetimes lighter. They have heretofore been generally more expensive buttheir use may, in the long term, be economical because of their greatlyreduced life cycle costs. Europeans have made bridges completely ofspecialty polymer matrix composite materials. The polymer compositematerials may be used as rebars, tensioning cables, in bonded sheets,wraps, decks, supports, beams or as the primary structures for bridges,decks or buildings. Structures made from polymer matrix materials arespecially effective in aggressive environments or are well adapted forbuilding structures where electromagnetic transparency may be needed forhighways, radar installations and hospitals.

As used herein, matrix composite materials may refer to generally anycontinuous matrix phase whether it comprises a settable constructionmaterial such as cementitious materials or a thermoplastic material suchas asphalt materials, as well as, other synthetic or natural highpolymer materials, ceramics, metals and other alloy materials. Thematrix composite materials include various fiber reinforcements thereindistributed throughout the matrix or placed at desired locations withinthe continuous phase. The matrix composite materials may be fabricatedas large building structures and load bearing shaped articles, or theymay be molded or machined as small parts for specialty uses. Forexample, the matrix material may comprise a thin sheet or web ofmaterial in the form of a foil, wrap, tape, patch or in strip form. Aspresently used in this specification, the term matrix composite materialdoes not necessarily refer to large civil engineering structures such ashighways and bridges.

In connection with the polymer and/or metal or ceramic matrix compositematerials, as well as, in the settable building materials such asconcrete materials, special problems cause structures made from thesematerials to become aged or damaged in use. More particularly, specialstructural defects arise in use including microcracking, fiberdebonding, matrix delamination, fiber breakage, and fiber corrosion, toname but a few. Any one of these microscopic and macroscopic phenomenamay lead to failures which alter the strength, stiffness, dimensionalstability and life span of the materials. Microcracks, for example, maylead to major structural damage and environmental degradation. Themicrocracks may grow into larger cracks with time and cause overallmaterial fatigue so that the material deteriorates in long-term use.

Advanced matrix composites used in structural applications aresusceptible to damage on both the macro-and microscopic levels. Typicalmacroscopic damage to composite laminates involves delaminations anddestruction of the material due to impact. On the micrographic scale,damage usually involves matrix microcracking and/or debonding at thefiber/matrix interface. Internal damage such as matrix microcrackingalters the mechanical properties of shaped articles made therefrom suchas strength, stiffness and dimensional stability depending on thematerial type and the laminate structure. Thermal, electrical andacoustical properties such as conductance, resistance and attenuationhave also been shown to change as matrix cracks initiate. Microcracksact as sites for environmental degradation as well as for nucleation ofmicrocracks. Thus, microcracks can ultimately lead to overall materialdegradation and reduced performance.

Moreover, prior studies have shown that microcracks cause both fiber andmatrix dominated properties of the overall composite to be effected.Fiber dominated properties such as tensile strength and fatigue life maybe reduced due to redistribution of loads caused by matrix damages.Matrix dominated properties on the other hand such as compressiveresidual strength may also be influenced by the amount of matrix damage.The impact responses of toughened polymer matrix composites have beenstudied and it has been shown that matrix cracking precedes delaminationwhich, in turn, precedes fiber fracture. Tough matrices which can reduceor prevent matrix cracking tend to delay the onset of delamination whichresults in an improved strength composite and longer lasting compositematerial.

Repair of damages is a major problem when these matrix compositematerials are employed in large-scale construction or advancedstructures. Macroscale damage due to delamination, microcracking orimpacts may be visually detected and can be repaired in the field byhand. Microscale damage occurring within the matrix is likely to goundetected and the damage which results from this type of breakdown maybe difficult to detect and very difficult to repair.

In order to overcome the shortcomings of the prior art construction andpolymer matrix composite materials, it is an object of the presentinvention to provide new and improved smart structural compositematerials having a self-healing capability whenever and wherever cracksare generated.

It is another object of the present invention to provide new andimproved composite materials including self-repairing reinforcing fiberscapable of releasing chemical agents into the local microscopic domainsof the matrix to repair matrix microcracks and rebond damaged interfacesbetween fibers and matrices.

It is a further object of the present invention to provide a new andimproved structural material.

It is another object of the present invention to provide a new andimproved cementitious material.

It is still a further object of the present invention to provide a newand improved cementitious or other construction composite materialhaving greater durability and greater tensile strength.

It is still another object of the present invention to provide a new andimproved matrix composite materials containing smart self-repairingfiber reinforcement containing repair chemicals therein which may bereleased by the smart fibers as needed in response to an externalstimulus, and optionally which may be refilled with additional repairchemicals as needed in the field.

SUMMARY OF THE INVENTION

In accordance with these and other objects, the present inventionprovides new and improved shaped articles comprising:

a shaped or cured matrix material having a plurality of hollow fibersdispersed therein, said hollow fibers having a selectively releasablemodifying agent contained therein, means for maintaining the modifyingagent within the fibers until selectively released and means forpermitting selective release of the modifying agent from the hollowfibers into the matrix material in response to at least onepredetermined external stimulus. In accordance with this invention theshaped articles are matrix composite materials of varying size and enduse applications. The cured matrix materials have within them smartfibers capable of delivering repair chemicals into the matrix whereverand whenever they are needed.

The present invention also provides a new and improved method forproviding shaped articles having long-term durability and environmentaldegradation resistance comprising the steps of providing a curablematrix composition, distributing a plurality of hollow fibers therein indesired manner so that the hollow fibers are disposed within the matrixmaterial in a desired predetermined distribution. The hollow fibers arefilled with a selectively releasable modifying agent therein which isnot released during the mixing or distributing step. The fibers arestructured so that the modifying agents stay within the interior spacesor cavities of the fibers within the matrix until the matrix is cured orset. After curing, the modifying agents are selectively released fromthe fibers by application or action of at least one predeterminedexternal stimulus.

In a preferred embodiment, the method of providing a improved durabilityshaped article comprises providing a cured matrix material containingsmart self-repair fibers reinforcement therein.

The principles of the present invention are applicable to space agepolymer, metal and/or ceramic structural matrix composite materials aswell as more conventional cementitious settable or curable building orconstruction materials.

Other objects and advantages will become apparent from the followingDetailed Description of the Preferred Embodiments, taken in conjunctionwith the Drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1f are schematic views of the new and improved self-repairingfiber reinforced matrix composite material in accordance with thepresent invention, illustrating a smart matrix repair sequence ofload-induced cracking, modifying chemical release and subsequentrebonding and repair of the fiber and matrix and wherein FIG. 1a showsthe smart fiber reinforced matrix composite prior to loading, FIG. 1bshows a lateral loading of the composite; FIG. 1c shows a crack formedthrough the smart fiber and matrix in response to the load, FIG. 1dshows release of modifying agent from the cracked smart fiber, FIG. 1eshows that the repair adhesive modifying agent flows to fill the cracksin the fiber and matrix, and FIG. 1f shows setting of the adhesive torebond fiber to fiber, fiber to matrix and matrix to matrix tostructurally repair the load induced cracking;

FIGS. 2a-2e are schematic views of the new and improved self-repairingfiber reinforced matrix composite material in accordance with thisinvention, illustrating a smart matrix repair sequence of salt or pHchange penetration into the matrix adjacent a smart fiber wrapped rebarreinforcement causing dissolution of the pH sensitive coating, therebyreleasing anticorrosion modifying agents in the domain or vicinity ofthe rebar to prevent corrosion of the rebar and showing the smart fiberwrapped rebar disposed in a matrix prior to chemical intrusion in FIG.2a, intrusion of chloride or carbon dioxide into the matrix and causinga pH change in the matrix in FIG. 2b, a breakdown of pH sensitivecoating on the smart fibers caused by pH changes in the matrix due tochemical intrusion in FIG. 2c, subsequent release of the anti-corrosionchemical from the smart fibers now rendered porous due to the breakdownof the coating in the viscinity of the rebar in FIG. 2d and illustratingreleased chemical corrosion protection chemicals around the rebar andpreventing corrosion of the rebar in FIG. 2e;

FIGS. 3a-3c are schematic views of the new and improved self-repairingfiber reinforced matrix composite material in accordance with thisinvention, illustrating a smart matrix repair sequence of freeze/thawprotection including freeze induced release of antifreeze from thefibers to provide an antifreeze-containing matrix to reduce freeze/thawdamage and showing a water-based anti freeze containing smart fiberreinforced matrix in FIG. 3a, a release of antifreeze from the smartfiber into the matrix upon exposure to lower temperatures caused byfreezing expansion of water based antifreeze in FIG. 3b and showing amatrix after release containing distributed antifreeze in FIG. 3c tolower freezing temperature of the matrix and reduce freeze thaw damage;

FIG. 4 is a schematic view of the new and improved smart fiberreinforced matrix composite material in accordance with the presentinvention, illustrating a release, repair mechanism in which the fiberis debonded from the coating and matrix in response to an applied loadto release the modifying agent from the uncoated fiber pores;

FIG. 5 is a schematic view of a smart fiber reinforced matrix compositematerial in accordance with this invention, illustrating a release,repair mechanism in which an applied load causes dimensional changes inthe fiber promoting release of modifier from the fiber into the matrix;

FIGS. 6a and 6b are schematic views of a new and improved matrixcomposite material in accordance with this invention, illustrating atwisted fiber bundle smart fiber matrix in FIG. 6a and illustratingrelease and repair from twisted fiber bundles, whereby compressiveloading causes unlocking of the twisted fiber bundles to releasemodifying agent into the adjacent matrix as shown in FIG. 6b;

FIG. 7 is a schematic view of a new and improved self-repairing fiberreinforced matrix composite material and system in accordance with thepreferred embodiment of this invention, whereby a smart fiber disposedwithin the matrix may be refilled with replacement modifier as needed bydrawing modifier into the fibers using a vacuum pump;

FIG. 8 is a schematic view of a fiber reinforced matrix compositematerial in accordance with another preferred embodiment of theinvention, illustrating a matrix containing a network of interconnectedsmart fibers into which additional modifying chemicals may be added fromthe exterior of the matrix in use;

FIG. 9 is a schematic view of the new and improved matrix compositematerial in accordance with this invention, illustrating a lightactivated release mechanism employing lasers;

FIG. 10 is a schematic view of the new and improved self-repairingmatrix composite material in accordance with this invention,illustrating a hydrostatic pressure induced release and repairmechanism;

FIG. 11 is a schematic view of a smart fiber reinforced matrix compositematerial wherein the modifying agents are released from the fibers byacoustic excitation;

FIG. 12 is a schematic view of a smart fiber reinforced matrix compositematerial of this invention, illustrating seismic or low frequencywave-induced modifying agent release mechanism;

FIGS. 13a and 13e are schematic views comparing the corrosion of rebarspossible with conventional cement rebar-reinforced matrices of the priorart, as shown in FIG. 13a, with the corrosion prevention provided by thenew and improved smart fiber matrices of this invention, shown in FIG.13e;

FIGS. 13b and 13f are schematic views illustrating a comparison of thepermeability of prior matrices, shown in FIG. 13b, with theimpermeability produced by the smart matrix permeability modificationagent release mechanisms in accordance with this invention shown in FIG.13f;

FIGS. 13c and 13g schematically illustrate the internal crackingproblems associated with prior art freeze/thaw damage to prior artmatrices, shown in FIG. 13c, in comparison with the antifreezecontaining smart matrix composite in accordance with this inventionshown in FIG. 13g;

FIGS. 13d and 13h illustrate the load-induced cracking schematicallyillustrated for a prior art matrix, shown in FIG. 13d, in comparisonwith the internally released crack prevention and filling smart fibermatrices in accordance with the present invention, shown in FIG. 13h;

FIG. 14 is a schematic view of a new and improved smart fiber having anotched wall configuration;

FIG. 15 is a schematic view of a new and improved smart fiber having abulging spheroidal portion and along its cross-sectional configuration;

FIG. 16 is a schematic view of a V-shaped smart hollow fiber inaccordance with this invention;

FIG. 17 is a schematic view of a double lumen smart fiber tubing inaccordance with this invention;

FIG. 18 is a U-shaped smart fiber tubing in accordance with thisinvention;

FIG. 19 is a schematic view of an alternate smart fiber configurationincluding an A-shaped tapering enlarged area along the length thereof;

FIG. 20 illustrates a coaxial concentric assembly of a polypropyleneinner hollow fiber surrounded by an outer brittle glass fiber inaccordance with a preferred embodiment;

FIG. 21 is a schematic view of a new and improved anticorrosioncomposite matrix in accordance with this invention, illustrating the useof redundant protective features to provide an enhanced anticorrosionreinforced concrete member;

FIGS. 22a-22d are schematic views illustrating the use of specialtypiezoelectric smart repair fibers to provide selective release andrepair of ionically charged ion modifying agents in response tocompressive loading;

FIG. 23a is a schematic view of an alternate embodiment of aself-repairing fiber reinforced matrix composite material in accordancewith this invention, illustrating the use of a smart matrix repair fiberwrapped rebar in combination with an impermeable barrier layer equippedwith sensors to detect changes in moisture, voltage or chloride ironconcentration within the matrix;

FIG. 23b is a schematic view of a preferred embodiment similar to FIG.23a wherein the impermeable barrier is employed as an electric chargeapplicator to permit an applied electrical signal to cause a release ofanticorrosion chemicals within the matrix adjacent a rebar;

FIG. 23c is a schematic view of the alternate embodiment similar toFIGS. 23a and 23b wherein a separate water barrier layer is employed asa first line of defense in combination with the hollow smart fibers inaccordance with this invention, which in turn contains water bindinghydroscopic chemical agent such as XYPEX, or the like;

FIG. 23d illustrates a special embodiment employing a separate electrodebarrier adjacent a rebar wrapped with the smart fibers which act tocreate a galvanic cell to release a water scavenging hydroscopicchemical when moisture intrusion is detected;

FIG. 23e is an alternate embodiment of the type shown in FIG. 23dwherein the electrode adjacent to the rebar is capable of causing smartfiber release of charged zinc ions to coat the rebar in anelectroplating operation to prevent corrosion of the rebar once theingress of water or moisture is detected;

FIGS. 24a and 24b schematically illustrate an alternate embodiment ofthe present invention wherein the smart fibers comprise a twisted pairof fibers embedded in the matrix, as shown in FIG. 24a, and whereinchanges in load on the matrix cause chemicals to be released from thetwisted pair of fibers as shown in FIG. 24b and illustrating that thetwisted pair of fibers may comprise optical fibers;

FIGS. 25a and 25b illustrate a schematic view of an alternate embodimentof a new and improved matrix in accordance with this invention,including an outer glass tube smart fiber having an optical fibertherein as well as a modifying adhesive chemical as shown in FIG. 25aand illustrating the release of adhesive due to cracking or maintainingthe optical fiber in an intact condition shown in FIG. 25b;

FIGS. 26a and 26b illustrate another preferred alternate embodiment ofthe invention, schematically illustrating an optical fiber which itselfis used as the smart fiber containing repair chemical therein and havingan optical fiber cladding layer along the periphery thereof as shown inFIG. 26a and showing in FIG. 26b schematically the change in lighttransmission properties caused by breakage of the outer glass fiber andleakage of the repair chemical to indicate that a fracture and releaseand repair have occurred;

FIGS. 27a and 27b show another alternate embodiment of this inventionwherein the smart repair fiber comprises an assembly of an outer glasstube and an inner metal fiber member in an optical fiber and an adhesivemodifying chemical therein as shown in FIG. 27a, which in response to anapplied cracking load ruptures the glass fiber to repair the crack whilemaintaining the optical fiber in an altered, but undamaged condition asshown in FIG. 27b;

FIGS. 28a-28c illustrate schematically optical fiber/smart fiberreinforcements for concrete matrices and demonstrate that the release,repair mechanisms may change the refracturing index transmissionproperties of the fluid so that the repair fiber itself may indicate thefact of rupturing repair and may also indicate the volume of the cracksfilled;

FIGS. 29a and 29b illustrate an alternate aspect of this preferredembodiment wherein septums or Brag optical gradings may be positioned atdesired locations along the length of the smart repair optical fiber asshown in FIG. 29a, which may aid in indicating the location of cracksalong the length of the fiber within the matrix as shown in FIG. 29b;

FIGS. 30a-30d illustrate a schematic view of an alternate embodimentwherein a smart fiber reinforcement comprises an optical fiber filledwith a repair chemical employing mirrors as shown in FIG. 30a to assistin locating where a crack damage has occurred as shown in FIG. 30b andshowing repair and rebonding of the repair chemical into the vicinity ofthe crack as shown in FIG. 30c and further showing in FIG. 30d theoptional replenishment of the repair chemical from an outside sourceusing a vacuum pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, new and improved shapedarticles comprise curable, settable, cross-linkable and/or hardenablematrix materials. The matrix material comprises a continuous phase andis a material that may be shaped to form a three-dimensional shapedarticle adapted for a particular use. Matrix materials can include anycurable, settable or hardenable materials used in construction,building, roofing, roadway, aircraft, automotive, marine, appliances,transportation and/or biomedical fields for making shaped articles.Typically these materials will be moldable or castable to form shapedobjects or may be laminated or assembled into finished products. Thematrix materials may be inorganic or organic in nature and may includeby way of illustration: cement, concrete, sintered fly ash or bottomash/phosphoric acid mixtures, ceramics including, for example, siliconoxide, titanium oxide, silicon nitrite, graphite, carbon, and metalssuch as aluminum, steel or other metal alloys, asphalt, thermoplasticpolymers, thermosetting polymers, thermoplastic elastomers,crosslinkable polymers, curable polymer resin systems andhydroxyapatite. Illustrative thermoplastic polymers include polyolefins,polyesters, polycarbonates, polyacrylates, polyarylates, polyamides,polyimides, polyaramides, polyurethanes, foaming polyurethanecompositions and any other thermoplastic polymers used as engineeringthermoplastics for making shaped articles. Thermosetting andcrosslinkable polymers and curable resin systems may include, forexample, one and two part epoxies, phenolformaldehyde resins and otherthermosetting and crosslinkable polymers. Thermoplastic elastomers caninclude rubbery polymers and copolymers including, for example withoutlimitation, styrene-butadiene, rubber, neoprene, SEBS, NBR, and, EPDMrubbers and the like. Visco-elastic materials and various latexmaterials may also be used. The matrix materials may also comprisesinterable ceramic materials including hydroxyapatites, as well as,other ceramic materials such as silicas, titanium, carbides, oxides andalumina. The matrix materials may also comprise metal matrices includingaluminum, iron, lead, copper, steel, bronze, phosphor bronze, brass andother alloys, as well as biomimetic systems like bone matrices formed ofvarious calcium salts, as well as other organic and inorganic materials.

The matrix materials in accordance with this invention are processableto form shaped articles by molding, casting, sintering, laminating,machining, extruding, or other material fabrication method useful withthe matrix material selected. The size and configuration of the finishedshaped article produced is essentially unlimited including various smallmachined parts to very large engineering construction panels for use inbuilding roadway and transportation applications. The matrix materialsmay be cured by means of catalysts, crosslinkers, radiation, heat,moisture, cooling or by any means used in this art for setting up,hardening, rigidifying, curing, setting or shaping these matrixmaterials to form shaped articles or objects.

The new and improved shaped articles of this invention additionallycomprise hollow fibers having interior spaces therein for containingselectively releasable modifying agents. The hollow fiber materials mayinclude inorganic fibers or organic fibers. Illustrative inorganicfibers include, without limitation: fiberglass fibers, cement fibers,asphalt fibers, hydroxyapatite fibers, glass fibers, ceramic fibers,metal fibers, and the like. Illustrative organic fibers that may be usedas the hollow fiber component may include, without limitation:polyolefin fibers, polyester fibers, polyamide fibers, polyaramidefibers, polyimide fibers, carbon fibers, graphite fibers, cellulosefibers, nitrocellulose fibers, hydrocarbon fibers, GORETEX® fibers,KEVLAR® fibers, and the like, to name but a few. Porous polypropylinefibers are a preferred hollow fiber. The hollow fibers may beelastomeric.

The fibers may be bundled, woven or loose. They may be held or engagedtogether with flexible web materials. They may comprise twisted pairsand additionally may include concentric structures of one or morefibers. The sidewalls of the fibers are typically rupturable or porousto permit the discharge or exiting of the modifying agent into thesurrounding cured composite matrix material. The fibers may come indifferent shapes, volumes, and wall thicknesses. They may be generallynotched, have periodic enlargements or bulges, V-shaped, double ormultiple lumens, U-shaped, or they may comprise combinations of one ormore different types of fibers. For example, double walled fibers areparticularly useful for two-part modifying compositions such as epoxies.Doubled fibers including a metallic inside fiber and a glass outersheath fiber are useful where bending of the metal fiber assists inbreaking the glass carrier fiber. Additionally, assembled structures ofpolypropylene hollow porous fibers disposed inside a glass outer fibermight be used to permit a first break and release of modifying materialto occur with the glass fiber and thereafter a secondary break andrelease of the polypropylene fiber at a later date to provide aspecially long-term profile modification to the shaped matrixcomposites. The smart-release fibers may also be paired or include otherspecialty fibers such as piezoelectric fibers or optical sensor fibersfor providing special monitoring, metering and diagnostic capabilities.Some of these specialty composites will be more particularly describedhereinafter. The fibers may also be woven together into a web so thatthey may be wrapped as an organized bundle around rebars or the like.Although fiber materials are preferred, other container-like smartrelease structures or vessels may be provided for special end uses. Forexample, in relatively large structural parts it may be useful to addthe repair chemicals in large flat balloons or bags layered or laid upwithin the matrix or layers of matrix. It should be apparent to thoseskilled in this art that for certain end uses, small release vesselshaving a shape somewhat different from hollow fibers for performing thesame smart release functions may be employed. In addition, the fibersmay be relatively small, chopped or comminuted fibers having lengths ofless than about one inch and diameters of less than about 100 microns.The fibers and matrices may be readily used in usual shaping processessuch as in an injection molding operations or the like.

In accordance with this invention, the hollow fibers include certaininternal modifying agents which are selectively releasable from thefibers in response to the application of certain predetermined externalstimuli. The modifying agents include agents which will modify theperformance characteristics of the cured shaped article matrix materialsin use. By way of illustration, the modifying agent may includepolymerizable monomers such as methyl methacrylates, styrene or otherpolymerizable starting materials. They may additionally include two partepoxies wherein an epoxy precursor material is disposed in one fiber orin one lumen of a double lumen fiber and the amine or othercross-linking agent is disposed in an adjacent fiber or in the otherlumen of the double lumen fiber. Other curable polymerizable monomersmay also be employed.

Another modifying agent which may be used herein includes a sealant usedto prevent water permeability and ingress or egress of water or otherliquid materials to and from the cured matrix composite. Illustrativeexamples for cement may include oily sealants to prevent ingress ofwater such as linseed oil or other known sealant materials.

Another important modifying agent for both cementitious and polymermatrices include adhesives which cure in situ to repair microcrackswithin the matrix in use. Illustrative adhesives include one- andtwo-part adhesives, one- and two-part epoxy adhesives, cyanoacrylateadhesives, Elmer's glue and others known to those skilled in the art.The adhesives may bond matrix to matrix, fiber to fiber, as well asfiber to matrix.

Certain water barriers are particularly useful modifying agents forcementitious matrices. These may include special ZYPEX® brand sodiumsilicate additives as well as siloxane and silica additives known asSALT GUARD® and the like.

Another modifying agent useful in the shaped articles of this inventionincludes anticorrosion agents such as calcium nitrite. These areparticularly useful in cementitious matrices employing rebarreinforcements or steel mesh reinforcements.

Another example of a modifying agent which may be disposed in theinterior of the hollow fibers for use herein includes antifreezematerial such as polypropylene glycol.

Fiber protectors may also be used as the modifying agents which can bematerials which protect the fibers themselves within the matrixmaterial. An example of this includes pH modifiers for protectingfiberglass in highly alkaline environments.

Still another class of modifying agents particularly useful in polymermatrices are solvents which permits solvent action to actually repairmicrocracking damage locally at a cracking site or possibly to dissolvethe matrix or fibers or both to permit them to re-form at a later time.

In addition to solvents, other curable monomers and co-monomers may alsoserve this repair function. pH modification agents may also be used asthe modifying agents, either alkali or acidic agents, which may beplaced in the interior of the fibers only to be released by anappropriate pH changes in the matrix. Other additives may include flameretardant agents. Visco-elastic polymers may also be used as modifiers.

Modifying agents for use herein may comprise rheological orelectrorheological fluids.

In accordance with this invention, means are provided for maintainingthe modifying agent within the hollow fibers. The modifying agents maybe physically trapped by, for example, drawing liquid additives into theinterior of the fibers and retaining them therein by capillary action orby closing off the ends of the fibers. For brittle fibers, sealing ofthe ends by heat or pressure may be one method for maintaining themodifying agents therein. Moreover, specialty coatings may be used,which will selectively degrade upon the occurrence of a particularexternal stimulus. Illustrative examples might include heat sensitivecoatings, pH sensitive coatings, ion sensitive coatings, and the like.These coatings are effective to close off the pores of the hollow fiberwalls or the ends of the fibers to prevent premature leakage of themodifying agent until the intended time. Illustrative coatings mayinclude waxes, low molecular weight hydrocarbon oils and coatingpolymers to name but a few. More particularly, the coatings may includechemically sensitive coatings, electrically sensitive coatings and/orradiation sensitive coatings. Chemically sensitive coatings may includemoisture sensitive coatings, pH sensitive coatings, ion sensitivecoatings or solvent sensitive coatings. Electrically sensitive coatingsmay include current sensitive coatings or voltage sensitive coatings.Radiation sensitive coatings may include light sensitive coatings,temperature sensitive coatings or radioactivity sensitive coatings.

In accordance with the present invention, means for permitting selectiverelease of the modifying agent in response to the external stimulus maybe provided. Illustrative examples include the selectively removable ordissolvable coatings which give way to permit leakage of the modifyingagent in response to, for example, stimuli such as heating, cooling,loading, impacting, cracking, water infusion, chloride infusion,alkalinity changes, acidity changes, acoustic excitation, low frequencywave excitations, hydrostatic pressure, rolling pressure, lightsensitivity or laser excitation, or the like. Electrical currents,voltages, electrorheological excitation, radiation, or other energeticstimuli may also be employed or effective to permit or cause selectiverelease of the modifying agent or agents from the fibers.

In accordance with this invention, the selective release of the modifieroccurs in the matrix when and where it is required and may lead toimproved toughness, strength, ductility, brittleness, permeability, fireretardancy, stiffness, dimensional stability, modulus of elasticity,fatigue, impact resistance, and other improved properties. Speciallyimportant in accordance with this invention is the ability to repairsmall microcracks forming in the reinforced matrix composites. Theselective release of the modifying agent may be chosen to be effectiveto rebond the fibers to the matrix, to repair the fibers themselves, toimprove or restore the matrix to fiber interface, to repairdelaminations, and to repair microcracks in the matrix itself which mayrepair or overcome cracking or corrosion induced dimensional weaknessesand ultimately reduced durability for the shaped articles.

In accordance with an embodiment, the shaped articles in accordance withthe invention include a plurality of modifying agent-filled hollowfibers present in an amount of less than about 10 volume percent of thematrix material.

Selective release of modifying agent may be provided in several ways.For example, when the hollow fiber is piezo-electric, pressurestimulation causes charging of the fiber which is effective to dischargeoppositely changed ions present in the modifying agent out of the fiber.Alternatively, electrical stimulation of a piezoelectric fiber causesthe fiber to constrict, thereby squeezing modifying agent out of thefiber. A hollow fiber of a shape memory alloy may respond to temperaturechange stimulation which causes the fiber to change shape therebysqueezing the modifying agent out of the fiber. Magnetic stimulationcauses magnetostrictive hollow fibers to constrict, thereby squeezingmodifying agent out of the fiber. In addition electrical stimulation ofelectrostrictive hollow fibers causes the fiber to constrict, therebysqueezing modifying agent out of the fiber.

As has been mentioned above, the shaped articles in accordance with thisinvention may be used for a number of applications, both large andsmall. Large construction applications are particularly preferred,particularly those used in harsh environments or for outdoor use.Illustrative end use applications for the new and improved shapedarticles in accordance with this invention include, for example withoutlimitation, structural sandwich panels, exterior applied insulationpanels, fire panels, construction building blocks, cements, concretes,fireproof doors, panels, walls, hazardous waste containment vessels,engines, concrete building blocks, roadways, bridges, dams, engines,road surfaces, roofing blocks, roofing shingles, decks for parkinggarages, and other building structures and columns. Other constructionapplications might include the use of these shaped, cured, smart-releasecomposites in bridges, post-tensioning cables, road decks, road deckoverlays, aircraft body components, including fuselages, wings and tipdesign, machined parts, helicopter blades as well as the aforementionedroofing structures.

The shaped articles of this invention might also be useful in biomedicalapplications as bone replacements as prosthetic devices and asbiomedical adhesives.

More particularly, shaped articles of this invention may be used to formself-growing structures. In accordance with this aspect of theinvention, the goal is to create a ceramic resembling bone which is anorganic-inorganic composite created at low temperature due to thepresence of organisms. Bone is made up of an oriented matrix which issecreted by bone forming cells referred to as osteoblasts. In naturalbone, organic matrices are made up of structural molecules which serveas a scaffolding and which are laid down in very precise, orientedpattern of fibrils into and onto which inorganic crystalline phasesform. The formation of the first crystals of inorganic salts of calciumphosphate are often referred to as initiation or nucleation which occursalong nucleation sites which appear at regular intervals along theorganic scaffolding, usually collagen laid down by osteoblasts. Oncenucleation has occurred, the next major process involves thecontinuation of crystalline growth from these nucleation sites outwardalong the fabric of the organic matrix and eventually between themolecules which serve as scaffolding. As crystal growth continues andforms against inorganic matrix, there is a loss of organic componentswhich are designed to reserve space in the matrix forever expanding theinorganic phase.

In accordance with this biological models, the present invention may beemployed to provided a self-growing structure something like bone,wherein the hollow pores polymer fibers may release chemicals and act asan organic template on which to form a strong structural bone-likecomposite. This self-growing structure might be used for structuralmaterials as well as for computer chips or for prosthetic devices. Moreparticularly, just as ligaments or tendons have been used as naturalmatrices to form bone materials, these polymer tubes or fibers are usedin accordance with the present invention to concentrate bone-likesubstances. The fibers are hollow and have porous walls. In accordancewith this invention chemicals are released from the hollow fibers,particularly polymeric materials which are designed to cause targetedrelease of water in an inorganic matrix to form a structural network ofcalcium phosphate materials. Instead of using collagen gels to form abackbone network, in accordance with this invention, a matrix materialincluding inorganic cementitious salts and a first polymer reactant maybe provided which includes hollow fiber materials including acondensable or cross-linkable moiety reactive with polymer. Underappropriate conditions, release of the co-reactant from the fiberscauses a condensation reaction of the matrix polymer in which water isproduced. The water byproduct of the condensation reaction is used tohydrate cement to build up a structural backbone along the fiberregions.

In accordance with another aspect of the invention, a hollow porouspolymer fiber material may be placed in a calcium phosphate materialmatrix in which a polymer powder monomer is present. A cross-linkingmonomer is then released from the fibers into the matrix. The ensuingcondensation polymerization reaction releases water, which then hydratesthe calcium phosphate materials. Xypex or other cement crystallizinginitiator materials may carry the hydration reaction away from thepolymer fiber scaffolding within the inorganic matrix. The structuralmake-up of these materials may be designed to resist stresses byincluding piezoelectric fibers within the matrix. Lines of force may begenerated by prestressing or stressing the piezoelectric polymer fibersalong which charged cementitious ions will migrate. This will cause thepolymer matrix to rearrange and the composite prestressing forcestherefore will generate an appropriate microstructure within thematerial.

Also in accordance with this aspect of the invention, self-healing maybe accomplished by leaving some of the original fibers void or by addingadditional fibers designed with specialty repair chemicals for repairingthe system. Hollow porous fibers may be used to deliver repair chemicalsat a later time if damage such as cracking occurs. Repair chemicals,either present as an adjuvant fiber additive or added to hollow fibersfrom the outside, may be used to improve the visco-elasticity of theentire component as desired.

In accordance with this invention, materials may be developed forapplication in self-repairing materials for use in facings, coatings andmembranes. In accordance with this aspect of the invention, the new andimproved fiber-containing matrix materials may be provided in the formof paints, membranes, roofing materials, or the like, includingself-repairing liquids within the fibers. The materials may be providedin the form of wraps for buildings, bridges, roads, or the like,including webs or fabrics of smart fibers disposed within the matrix.Repair chemicals may repair cracks in the wrap itself or also seep intoand repair adjacent structures to which the wrap is adhered to improvethe overall structural performance over time. Specialty wraps includingsolar collecting fibers might also be added to the exterior ofpreviously existing outdoor structures.

Another biological or biomedical application for the new and improvedshaped articles of this invention might include smart-release bandages,artificial skin materials, poultices, bandaids and the like whichinclude smart fibers which release healing chemicals or healingpromoting chemicals by upon movement of the patient or by application ofanother stimulus, such as for example, a heating pad, or the like. Thesmart fibers used in these bandage applications might include suchrelease chemicals as oxygen releasing chemicals, moisturizers, aloevera, antibiotics, anti-inflammatants, analgesics, non-stick agents orthe like.

Another illustrative use of the shaped articles of this invention mightbe polymer matrices including smart fibers therein which may be made toinclude dissolving chemicals which ultimately assist in de-naturing,degrading or destroying the polymeric structures by depolymerization orchemical reaction to improve recyclability of the polymer material.

The shaped articles of this invention may also be used in various smallshaped article applications including aerospace applications, piperepair, engine pistons, rubber matrices, waterborne paints and coatings,rubber gasket materials and other seals and in woven fabrics. Forexample, in fabrics the fibers may contain a fabric glue to repair smalltears or abrasions of the fabric. Hard self-repairing shaped articles,such as silicon nitride fibers in carbon-alumina matrices for pistonsmight be used. Metal matrices that may be employed include metals andalloys such as alumina as well as foamed metals. The fibers for thesemetallic composites may include adhesive materials or corrosionresistant materials to help repair the matrices or other desirable smartrelease additives.

The new and improved smart fibers of the present may be disposed withinlarge cross-sectional areas or sections of a matrix prior to cure whichmay thereafter be used to release curing agents from several positionsdisposed throughout the curable matrix simultaneously to speed up orassist in the curing of large cross-section polymer articles. Similarly,natural fibers such as wheat straws or the like may be added to concreteor adobe matrices to stabilize the composites so that they do notcrumble or flow in use.

In a related application, the new and improved smart matrix materialsmay be used to perform road repair and pothole repair. In connectionwith this aspect, smart release fiber-containing uncured material may beadded to a pothole. An agitation or pressure may be used to releasecurative agents from the interior of fibers provided in the matrixmaterial to promote adhesion and curing of the pothole repair mass tothe substrate road surface. Additional fibers may be provided containingrepair adhesives which release in response to tire pressure, to furtherstrengthen and reinforce the pothole patch in use.

Another highway application of the present invention includes the use ofsmart release fibers to add phosphorescent chemicals to concrete orasphalt matrices. Phosphorescent roads may clearly demarcate the road orhighway surface from non-road driving surfaces at night without the needfor street lights or other markers or reflectors. The smart matrixmaterials would permit renewed release of phosphorescent agents into theroad surface, as the layers of the road surface are worn away by highwaytraffic. A continually replenishing supply of chemicals that couldabsorb sunlight during the day and re-emit it as phosphorescent light inthe evening hours would be provided.

In accordance with another aspect of this invention, the shaped articlesmay include hollow and continuous matrix formed into a shaped articleand having hollow fibers therein which permit visual inspection of thestructural part in use. The use of hollow, air-filled fibers permitspersons to actually look into and see inside the matrix to see cracksnear the fibers. These hollow fibers also permit exterior introductionof chemicals to be performed to add chemicals to a previously curedmatrix.

Hollow or filled fibers may be provided with dyes or other sensing orsensible materials to identify the presence of structural stresses orweaknesses and also the locations of these stresses in large structuralarticles. For example, release of dyed materials from fibers may permitthe dye to migrate to the surface to indicate a structural compromise orrepair need in a highway, bridge, or the like. Specialty dyes such asX-ray sensitive dyes may be added to help diagnose a smallmicrostructural repair problem. More particularly, if the dye is leakedinto the matrix in use due to structural damage, periodic diagnosticteams may test with high energy beams shined into the matrix. Theinteractive dye would signal back after excitation in a detectablemanner so that the need for attention or repair would be revealed.Piezoelectric fibers may also be used to evaluate the state of thematrix. Remote sensing of eddy currents or electrical or magnetic fieldsgenerated about the fibers in response to pressures or stress may bedetected in a matrix in these ways.

Still another application for the shaped articles of this invention caninclude non-biological but biomimetic materials wherein a polymer matrixcontaining crystallizable mineral elements such as alumina alkoxide maybe provided. A condensation reactive element or ingredient providedinside the smart fibers may be released on application of appropriateexternal stimulus from the smart fibers within the matrix containing thealumina crystals. The by-product water of the condensation reaction inthis case may be used to cause alumina crystals to grow at specifiedlocations within the shaped article.

Another special useful application of the shaped articles in accordancewith this invention is as a containment structures for radioactive orchemical waste materials. In accordance with this aspect, fibersprovided with chemically sensitive coatings or radiation sensitivecoatings may be provided which are adapted to release scavengercompounds when radiation or chemical waste is detected. The compoundswill then migrate from the fibers into the matrix to scavenge and renderharmless radioactive or chemical materials leaking into the containmentvessels to prevent them from being discharged from the containment areainto the environment. Alternatively, permeability modifying agents maybe released from the coated fibers to boost the impermeability of thecontainment vessel to waterborne contaminants.

The new and improved shaped articles of this invention may be employedto form self-repairing impact resistance layers in laminated materialsand structures. For example, a clear, transparent polymer matrixcontaining adhesive filled glass fibers may be used as an interlayerbetween two safety glass or polymer sheets. Impact fracture of a basesheet will cause local release of repair adhesive from the interlayer tocontrol fragmentation and rebond cracked or fractured sections of alaminate.

As has been mentioned above, various means may be provided to force therepair chemicals out of the fibers. Chemicals may be pumped into hollowfibers from the outside or propellant gases may be injected intopreviously filled fibers to which external access has been provided toforce the chemicals out. Other methods to promote repair chemicalrelease may include electrical, magnetic, and chemical means which alterthe shape, permeability or coating integrity of the fibers. Shapedmemory alloy materials may be used as the fiber or these materials maybe used in the fiber to squeeze the fiber and thereby pump the chemicalsout. Fibers which change their shape in response to applied light ormagnetic forces or fields may also be used to discharge the chemicals asdesired.

The smart release shaped articles and materials in accordance with thepresent invention may be used throughout building structures to provideearthquake proof buildings which can withstand seismic activity withreduced hazard and damage. This is accomplished by preventing flyingdebris from being created and by supporting building structures inmatrices adapted to visco-elastically respond to seismic vibration.

Because the beneficial improvements provided by the new composition,articles and methods of this invention may be useful for broad range ofapplications, it is difficult to specifically enumerate each of them.The present invention will be further illustrated by several specificend use applications provided to further illustrate the improvementsprovided by the present invention.

Referring now to FIGS. 1a-1f, the new and improved self-repairing fiberreinforced matrix composite and its operation in the field is shown. Asdepicted in FIG. 1, a hollow fiber containing an adhesive modifyingagent and coated with a thin coating material is dispersed within asettable or curable matrix material which may be either a polymer orcementitious material. As shown in FIG. 1b, a loading applied to ashaped article causes strains within the matrix, which in turn cause thefiber to break and the matrix to crack. This causes the modifyingchemical agent disposed within the hollow fiber to be released into thevicinity of the crack in the matrix as shown in FIG. 1b. The modifyingagent flows and fills the void as shown in FIG. 1e and eventually curesto rebond the fiber to the matrix and to repair the fiber to itself asshown in FIG. 1f. This schematically illustrates the modified fiberconcept of the present invention.

Referring now to FIGS. 2a-2e, a similar smart fiber repair embodiment isdepicted wherein the smart hollow fibers contain anticorrosive modifyingagent and are coated with fibers which are pH sensitive. These smartfibers are disposed within the matrix adjacent the rebar reinforcementby selectively positioning them adjacent the rebar as the matrix ispoured into the concrete mold or the rebar can actually be wrapped withthe hollow fibers which have been previously banded together as a web ortape. In accordance with this matrix composite construction, theanticorrosion filled smart fibers are disposed immediately adjacent therebars. The anticorrosive chemical compounds are not released to protectthe rebars unless or until the exchange has occurred in the vicinity ofthe rebar, either due to chloride iron infiltration or carbon dioxideintrusion. The advance of corrosive chemicals breaks down the pH versussensitive coating on the smart fiber, releasing the protectiveanticorrosive agent to protect the rebar from corrosion by theenvironmental chemicals found in FIGS. 2c-2e.

Referring now to FIGS. 3a-3c, the smart fiber matrix is shown inoperation in plain and in antifreeze modifying agent disposed within thehollow fibers. A water-based antifreeze expands as it cools to force itsway out of the pores in the hollow fiber, thereby dislodging thecoating, if present, and permitting the antifreeze to exit into thelocal environment of the matrix. As shown in FIGS. 3b-3c, the release ofthe antifreeze into the matrix lowers the freezing temperature ofmoisture in the materials within the matrix preventing freeze/thawdamage from occurring to the matrix.

Referring now to FIG. 4, a debonding of a coated fiber is shown as amechanism for releasing the modifying agent contained within the smartfiber into adjacent areas of the matrix. This can occur, for example,where there is coating applied to the smart fiber to retain themodifying agent within the fiber interior as a higher affinity for thesurrounding matrix in a cured state than to the fiber. Accordingly,debonding of the fiber from its coating allows the pores to become opento permit chemical release.

Referring now to FIG. 5, there is illustrated in the embodiment whereinmodifying agent release is caused by torting, twisting or other loadchanges which cause a dimensional change in the shape of the hollowfiber, which in turn forces the modifying agent out into the surroundingmatrix. These torting, twisting or other loads placed on the fiber maycause local debonding of the fiber from its coating, permitting releaseas shown in FIG. 4 or a mechanical forcing of the contents of the fiberthrough the pores, which in turn causes dislodgment of the coating mayalso occur.

Referring now to FIGS. 6a and 6b, the application of the compressiveload on a twisted fiber bundle can cause debonding of the coating fromthe twisted fibers forcing fluid contained within the hollow spaces ofthe fiber through the fiber pores and into the surrounding matrix.

Referring now to FIG. 7, a preferred embodiment of the present inventionincludes providing the smart hollow fiber reinforcement within a matrixso that end portions of the fiber are accessible from the exterior ofthe matrix to permit additional modifying agents to be supplied into thefibers of the matrix. As depicted therein, a reservoir of modifyingagent may be placed in the fiber and a vacuum pump may be attached tothe opposed ends to draw the modifying agent into the fibers toreplenish any leaked materials therein.

FIG. 8 is an extension of the concept described and schematicallyillustrated in FIG. 7 wherein a series of hollow smart fiberreinforcements are arranged in a continuous network to permit theadditional chemicals to be added from the outside throughout the entirematrix.

Referring now to FIG. 9, other mechanisms may be employed for dislodgingor releasing the modifying agent into the surrounding matrix at aselected time after curing, such as, by example, using laser energy tocause an aneurysm to form in the fiber which permits leakage.

Referring to FIG. 10, hydrostatic pressures may also cause the fiberdiameter to be locally reduced, causing an exiting of the modifyingagent into the surrounding matrix.

FIG. 11 shows an embodiment wherein acoustic excitation is employed asthe means for releasing the modifying agent from the fiber.

FIG. 12 is an alternate embodiment wherein waves of low frequency suchas seismic waves may pass through the matrix in such a manner as tocause debonding of the fiber from a coating or uncoated fibers may causethe modifying agent to exit from pores disposed within the fiber matrixdisposed within the hollow fiber.

FIGS. 13a through 13h demonstrate in a side-by-side comparison theability of the smart fiber reinforced matrix composite materialsprepared in accordance with this invention to prevent environmentaldistress and aging frequently encountered by prior art compositematerials. A comparison of FIGS. 13a and 13e shows that the modifyingagent in FIG. 13e is an entire corrosion agent to prevent corrosion ofthe rebars and in that case calcium nitrite is preferred.

In FIGS. 13b and 13f the permeability of the matrix may be controlled bysetting up a polymerized polymer within the matrix as shown in FIG. 13fto prevent permeability. This may be effected in several ways, and inone preferred embodiment, polymerizable components are freely mixedwithin the concrete which require only the exposure to a liquid catalystto cause them to set up into an impermeable barrier. FIGS. 13c and 13gillustrate the release of antifreeze materials in FIG. 13g to preventfreeze/thaw and to brittleness and cracking due to ice crystalsformation within the matrix from occurring. Finally, FIGS. 13d and 13hillustrate the development of local microcracks due to local loadingwhich may be locally repaired by release of repairing adhesives as inFIG. 13h to fill cracks or voids and rebond fibers and matrices adjacentmicrocracks to prevent major microscopic failures from occurring.

In accordance with this invention, the smart fiber hollow fibers used tomake the smart fiber reinforcements in accordance with this inventionmay have any desired configuration. As illustrated in FIGS. 14 through20, a wide variety of cross-sectional configurations may be employed, aswell as multi-lumen tubes and multiple concentric tube assemblies may beemployed.

Referring now to FIG. 21, the new and improved smart fiber matrixcomposite materials in accordance with this invention may be used inconnection with other matrix protecting practices to provide redundantprotection against environmental damage. As depicted in FIG. 21, acementitious matrix including rebars may include surface coatings andsealants to prevent the ingress of harmful environmental liquids.Calcium nitrite anticorrosion chemicals may be freely mixed within thecement and the smart fiber reinforcements may be disposed immediatelyadjacent the rebar containing additional anticorrosive modifying agentsin accordance with this invention for release as needed when theconcentration of corrosion chemicals get sufficiently high to stimulatetheir release.

Referring now to FIGS. 22a through 22d, there is depicted a specialembodiment of the present invention wherein the notion of smart fiberrelease and repair is coupled with specialty fibers. As depicted in FIG.22a through 22d, the smart fiber itself comprises a piezoelectric fiberinto which a liquid chemical is first applied or deposited by providingan electric current to the piezoelectric components of the fiber. Themodifying chemicals accretes within and on the surfaces of the web offibers making up the solid piezoelectric cylinders, which in turn hollowfibers which may be placed and disposed within the matrix. In accordancewith these embodiments the modifying agents are released from thepiezoelectric fibers by the application of service load stresses on thematrix. These generate electrical charges in the piezoelectric fibersdue to their piezoelectric character. The electrical charges causepositive ions to move from inside the porous fibers into the surroundingmatrix. Negative ionic materials located in the matrix may also be drawninto or attracted to the piezoelectric hollow fiber. In this way repaircan be done by dispersing charged ions into the matrix or may through byselectively drawing undesired materials into the fibers to remove themand causing damage to the matrix.

Referring now to FIGS. 23a through 23d, another specialty applicationfor the smart fiber reinforced matrix materials in accordance with thisinvention is shown, which include an impermeable barrier equipped withsmart sensors in addition to a hollow fiber wrapped rebar composite inaccordance with this invention. The impermeable barrier may be connectedto sensor equipment shown as a feedback loop capable of detectingingress of moisture, changes in voltage or changes in chloride ironconcentration.

As shown in FIG. 23b, once the ingress of moisture is sensed at theimpermeable barrier layer, an electrical signal may be sent through theinner barrier layer, causing discharge or migration of cat ions from themiddle layer towards the rebar, which causes a coating on the smartfiber to be broken down to permit release of the modifying agentcontained therein of anticorrosion chemicals into the immediate vicinityof the rebar to prevent corrosion.

As depicted in FIG. 23c, the hollow smart fibers in accordance with thisinvention are disposed in a region bounded by the barrier layer on oneside and the rebar on the other to provide redundant back-up protectionto the rebar to prevent corrosion. More particularly, the hollow fiberscontain water binding chemicals which effectively remove the damagingwater from reaching the rebar in that intermediate region, therebypreventing corrosion.

In FIG. 23d, an alternate aspect is provided wherein the barrier iselectrified to provide a galvanic cell in the immediate region betweenthe barrier layer and the rebar. A counter galvanic cell is createdabout the hollow middle fibers which contain a modifying chemical insidethe buffer zone, which in turn can release moisture binding hydroscopicchemicals in response to application of electrical charges or mayrelease anticorrosive chemicals. In accordance with FIG. 23e, the hollowfibers disposed within the barrier buffer zone may include zinc ionswhich will migrate and coat the rebar in a galvanizing or electriclading action by application of the voltage between the barrier andrebar.

Referring now to FIGS. 24 and 24b, another specialty embodiment of theinvention includes the use of optical fibers as the self-repairing fiberwhich in turn contains a modifying chemical which may be positionedwithin the matrix. Twisted pair fibers, for example, may be used asshown in FIGS. 24a and 24b. In response to the application of appliedloads, the optical fibers may be changed in their transmissionproperties indicating a break or leak in the matrix and may in turn becaused to discharge their internal modifying agent into the surroundingmatrix to, for example, repair a microcrack as shown in FIG. 24d.

FIGS. 25a and 25b depict a similar embodiment involving the use of glasshollow fibers as surrounding hollow fibers for containing adhesiverepair modifying agents and for housing an optical fiber therein. Asshown in FIG. 25b, microcracking of the matrix causes release of therepair adhesive locally within the matrix to prevent further crackingand breaking which might damage the optical fiber and its transmissioncapability.

Referring now to FIGS. 26a and 26b, a different use of optical fibers asthe smart fibers in a matrix composite in accordance with this inventionis shown. More particularly, a cladded optical fiber having an interiorcavity filled with an adhesive repair chemical is provided in asurrounding polymer or cement matrix. The light transmission of theintact fiber is of a given value. Once applied, loads are causedcracking and bending of the matrix as shown in FIG. 26b which will causebending of the fibers decreasing the amount of light transmittedtherethrough.

Referring now to FIGS. 27a and 27b, another glass fiber embodiment isshown wherein an assembly including an outer hollow glass tube filledwith adhesive modifying agent and including an optical fiber therein anda middle fiber therein provide a special matrix composite. As shown inFIG. 27b, in response to an applied load, the middle fiber bendingassist in breaking the outer glass tube to thereby release the repairingadhesive to the matrix. The optical fiber polymer may be bent orstretched and light lost to cladding coating on the fiber may bedetected outside the matrix to determine bending of the fibers andpossible microcracking therein.

Referring now to FIGS. 28a through 28c, another use of an optical fiberfor forming the smart repair fibers in accordance with this inventionillustrates reliance on release of the repair chemicals within theoptical fiber to change the optical characteristics to indicate thatmicrocracking has occurred wherein the change in volume of the repairmaterial can indicate the volume cracks that needed to be filled and thechange in refracturing index of light transmitted through the fiber mayalso give an indication of the volume of the cracks that have beenfilled in accordance with this invention.

Referring now to FIGS. 29a and 29b, a plurality of septums or bragoptical gradings may be positioned along the modifying agent filledoptical fiber in accordance with this invention to permit the diagnosticdetection of the location of cracks by noticing changes in therefracturing index located between gradings. FIGS. 29a and 29billustrate a further preferred embodiment employing optical fibers asthe hollow fiber component of the smart matrix materials in accordancewith this invention. The elongate optical fiber is subdivided intolongitudinal segments by dividers or septums over brag optical gradingswhich maintain the optical transmission characteristics along the fiberwhen filled with the chemical modifying agents. As depicted in FIG. 29b,in the event of a breakage and leaking of the repair chemical into theadjacent matrix, the dividers or septums limit the quantity of fluidloss to a local segment only. The change in optical characteristics inthat local segment will still serve to identify the location of thecrack, while preventing an overall loss in all of the fiber fluidcontents.

Referring to FIGS. 30a-30d, still another optical fiber hollow fiberembodiment of this invention is depicted employing fibers ofpredetermined longitudinal length or dimension having a mirror end wellat one end thereof and having repair chemical disposed therein. Checkson the integrity of the optical fiber segment can be made byintermittently sending an optical pulse along the short length of thefiber and bouncing it off the mirror and comparing the reflectedintensity to the transmitted intensity to determine whether or not therehas been a change along the length of the fiber. By placing a mirrorintermediate the length of a row of fiber, the fiber sensing the opticalsensing test could be performed from either end and in that manner thelocation of the break on one side of the mirror or the other could bedetermined.

Referring now to FIG. 30c, the new and improved smart matrix material isshown in a rebonded condition wherein the interior modifying agent, inthis case an adhesive, has leached into the surrounding matrix to repaircrack, to bond the matrix to itself, and to bond the coating to thematrix and the coating to the fiber. This restores the overall integrityof the composite, and in some cases, may lead to actual increases inoverall strength and performance for the rebond material.

FIG. 30d illustrates the exterior refilling design in accordance withthe preferred embodiment for vacuum pump refilling of a broken opticalfiber to repair or restore optical transmission service therealong.

In accordance with the present invention, other embodiments for usingthe self-repairing fiber reinforcement smart matrix composite matrixmaterials described herein will be readily apparent to those skilled inthis art. For example, employing ceramic matrices such as ahydroxyapatite ceramic minerals and reinforcing hollow fibers containingbio-compatible crack repairing adhesives may be used in jointreplacements or as shaped articles for prosthetic devices. In thismanner, biomedical embodiments for the smart matrix composite materialspossessing the self-repair properties may be used to provide improved orextended fuselage to prosthetic devices and bone replacements. Stressload fractures occurring within the artificial bone or joint segmentwill self-repair in accordance with the principles of this invention.

In still another embodiment of the present invention, the overallmatrices may be used in building applications to provide some seismicresistance or earthquake-proof properties to the structures. Moreparticularly, the response of a solid matrix material containingrigid-filled fibers or liquid-filled fibers may vary in response toseismic waves. Reological fluids and electroreological fluids are knownwhich are stiff in one condition, and thereafter upon application ofelectrical current, may become fluid or liquid. These fillings withinreinforcing fibers may be intentionally changed periods of seismicactivity in response to, for example, a sensor switch to liquefy orfluidize building structures to better withstand seismic vibrationactivity without causing brittleness. In the liquefied electroreologicalstate, the overall matrix composite may be better able to withstandenergy vibration than might be encountered in the solid rigid compositestructure.

In still another aspect of the invention, it is known that alkalireactions are sometimes caused within cementitious matrix materials whenaggregate reacts with matrix causes an expansion of the aggregateagainst the matrix. This causes internal stresses to develop within thematrix composite or shaped article, which usually appears as crackswithin the matrix. The use of the smart fibers in accordance with thepresent invention containing adhesives will repair some of these cracks.In addition, instead of adhesives these smart fibers may be filled withpH modification agents such as acidic agents to neutralize the alkalireaction. In addition, fibers filled with the alkali reaction inhibitingacidic modifying agent may be used in combination with the matrix repairadhesive filled smart fibers in accordance with this invention.

In accordance with this invention, the matrix selected may vary, forexample, RIBTEC® mats of stainless steel fibers may be slurryinfiltrated with cement, hollow fibers for repair may be included. Underloading, the mat causes the cement to form microcracks, which inaccordance with this invention releases the repair adhesives into thematrix to provide a repaired high toughness composite material.Depending on the matrix selected, different fiber properties may bedesired, for example, in rigid matrix materials such as cementitious setmaterials or sintrex ceramic materials more flexible fibers may bedesirable, whereas in polymer matrices having inherent elasticity orflexibility, more rigid fibers such as glass or metal fibers may bedesired. In addition, it may be desired to use fibers which becomebrittle over time. Fibers may be connected to each other with flexibleparts to ensure that they do not break prematurely during mixing orcompounding. Furthermore, chemicals which survive the long periods oftime and which survive repeated temperature variations may also be usedas the modifying agents. Although several different matrix materialshave been disclosed or suggested herein, others may still be used bythose skilled in this art. Although a number of different kinds offibers have also been described, still other fibers might also be usedby those skilled in this art in accordance with the principles of thisinvention. Different modifying agents and different mechanisms forselective release of the modifying agent in response to an externalstimuli or internal stresses caused by other external occurrences mightalso be developed and designed by those skilled in the art given theprinciples provided herein. Accordingly, all such obvious modificationsmay be made herein without departing from the scope and spirit of thepresent invention as defined by the appended claims.

I claim as my invention:
 1. A shaped article comprising:a shaped articlecomprising a continuous phase of a shaped matrix material and a secondphase comprising a modifying agent, said modifying agent being effectiveto change a response of the shaped article to an external stimulus, suchthat upon being exposed to the external stimulus, the continuous phaseis less structurally damaged by being exposed to the external stimulusas compared to a similiar shaped article not containing said modifyingagent second phase.
 2. A shaped article as defined in claim 1, whereinsaid second phase comprises at least one hollow fiber having themodifying agent contained therein.
 3. A shaped article comprising:ashaped article comprising a continuous phase of a shapeable matrixmaterial including at least one hollow fiber disposed therein, saidhollow fiber having a modifying agent contained therein, said modifyingagent being effective to alter a response of the shaped article tovibrational excitation so that the shaped article can withstandvibrational excitation without becoming brittle.
 4. A shaped article asdefined in claim 1, wherein said modifying agent comprises a phasechange material selected from viscoelastic polymers, rheological fluidsand electrorheological fluids.